47 



Abstract— Between June 1995 and May 

 1996 seven rookeries in the Gulf of Cali- 

 fornia were visited four times in order 

 to collect scat samples for studying spa- 

 tial and seasonal variability California 

 sea lion prey. The rookeries studied 

 were San Pedro Martir, San Esteban. 

 El Rasito, Los Machos, Los Cantiles. 

 Isla Granito, and Isla Lobos. The 1273 

 scat samples collected yielded 4995 

 otoliths (95.3%) and 247 (4.7%) cepha- 

 lopod beaks. Fish were found in 97.4% 

 of scat samples collected, cephalopods 

 in 11.2%, and crustaceans in 12.7%. We 

 identified 92 prey taxa to the species 

 level, 11 to genus level, and 10 to family 

 level, of which the most important were 

 Pacific cutlassfish (Trichiuruslepturus), 

 Pacific sardine (Sardinops caeruleus), 

 plainfin midshipman (Porichthys spp. ), 

 myctophid no. 1, northern anchovy 

 (Engraulis mordax). Pacific mackerel 

 (Scomber- japonicus), anchoveta (Ceten- 

 graulis mysticetus), and jack mackerel 

 (Trachurus symmetricus). Significant 

 differences were found among rooker- 

 ies in the occurrence of all main prey 

 (P<0.04), except for myctophid no. 1 

 (P>0.05). Temporally, significant dif- 

 ferences were found in the occurrence 

 of Pacific cutlassfish, Pacific sardine, 

 plainfin midshipman, northern an- 

 chovy, and Pacific mackerel (P<0.05). 

 but not in jack mackerel lx 2 =2.94, df=3, 

 P=0.40 1, myctophid no. l(;r= 1.67, df= 3, 

 P=0.64 ), or lanternfishes ( x 2 =2.08, df=3, 

 P=0.56). Differences were observed in 

 the diet and in trophic diversity among 

 seasons and rookeries. More evident 

 was the variation in diet in relation to 

 availability of Pacific sardine. 



Spatial and temporal variation in the diet 



of the California sea lion (Zalophus californianus) 



in the Gulf of California, Mexico 



Francisco J. Garcia-Rodriguez 



David Aurioles-Gamboa 



Centra Interdisciplinary de Ciencias Mannas-lnstituto Politecnico Nacional 



Departamento de Biologia Manna y Pesquerias 



Apdo. Postal 592 



La Paz, Ba|a California Sur, Mexico 



E-mail address (for F J. Garcia-Rodriguez) fjgrodriifflcibnor.mx 



Manuscript approved for publication 

 9 October 2003 by Scientific Editor. 



Manuscript received 20 October 2003 

 at NMFS Scientific Publications Office. 



Fish. Bull. 102:47-62 (2004). 



The population of the California sea 

 lion (Zalophus californianus), in the 

 Gulf of California numbers approxi- 

 mately 23,000 individuals, 82% of 

 which inhabit the northern region of 

 the gulf above latitude 28° (Aurioles- 

 Gamboa and Zavala-Gonzalez, 1994). 

 In this region are found the most 

 important reproductive areas and the 

 highest pup production of the Gulf. 

 Aurioles-Gamboa and Zavala-Gonzalez 

 (1994) suggested that the high con- 

 centration of animals in this region is 

 related to high abundance of pelagic 

 fish such as Pacific sardine (Sardinops 

 caeruleus) (also known as South Ameri- 

 can pilchard, FAO), Pacific mackerel 

 (Scomber japonicus). Pacific thread 

 herring (Opisthonema libertate), and 

 anchoveta (Cetengraulis mysticetus) 

 (Cisneros-Mata et al., 1987 1 ; Cisneros- 

 Mata et al., 1991 2 ; Cisneros-Mata et al., 

 1997 3 ). 



Despite the importance of the north- 

 ern gulf region, feeding studies of the 

 California sea lion at Gulf of California 

 rookeries have been few and have been 

 conducted at different time periods. 

 Researchers have studied sea lion diet 

 in Los Islotes (Aurioles-Gamboa et al., 

 1984; Garcia-Rodriguez, 1995), Los 

 Cantiles (Isla Angel de la Guarda), Isla 

 Granito (Sanchez-Arias, 1992; Bautista- 

 Vega, 2000), and Isla Racito (Orta-Davi- 

 la, 1988). These studies have shown that 

 sea lions consume a variety of prey and 

 that differences exist between the diet 

 of sea lions found at different rookeries 

 within the Gulf of California. At Los 

 Islotes, the most important prey were 

 cusk eel (Aulopus bajacali), bigeye bass 



(Pronotogrammus eos), threadfin bass 

 (Pronotogrammus multifasciatus), and 

 splitail bass (Hemanthias sp.) (Aurioles- 

 Gamboa et al, 1984; Garcia-Rodriguez. 

 1995). At Los Cantiles and Isla Granito 

 important prey were lanternfish (Dia- 

 phus sp.), northern anchovy (Engraulis 

 mordax). Pacific cutlassfish (Trichiurus 

 nitens), shoulderspot (Caelorinchus 

 scaphopsis), and Pacific whiting (Mer- 

 luccius productus) (Sanchez-Arias, 

 1992; Bautista-Vega, 2000), whereas at 

 Isla Racito, important prey were Pacific 

 sardine (Sardinops caeruleus). Pacific 

 mackerel (Scomber japonicus), grunt 

 (Haemulopsis spp.), rockfish (Sebastes 



1 Cisneros-Mata, M. A.. J. P. Santos-Molina, 

 J. A. DeAnda M.,A. Sanchez-Palafox, and J. 

 J. Estrada. 1987. Pesqueria de sardina 

 en el noroeste de Mexico ( 1985/86 ). Informe 

 Tecnico, 79 p. Centro Regional de Inves- 

 tigaciones Pesqueras de Guaymas. INP. 

 SEPESCA. Calle 20 No. 605 Sur Col. La 

 Cantera. Guaymas, Son. CP. 85400. 



2 Cisneros-Mata, M. A., M. O. Nevarez- 

 Martinez, G. Montemayor-Lopez, J. 

 P. Santos-Molina, and R. Morales- 

 Azpeitia. 1991. Pesqueria de sardina en 

 el Golfo de California de 1988/89-1989/90. 

 Informe Tecnico. 80 p. Centro Regional de 

 Investigaciones Pesqueras de Guaymas. 

 INP. SEPESCA. Calle 20 No. 605 Sur Col. 

 La Cantera. Guaymas, Son. CP. 85400. 



3 Cisneros-Mata, M. A., M. O. Nevarez- 

 Martinez, M. A. Martinez-Zavala, M. L. 

 Anguiano-Carranza, J. P. Santos-Molina, 

 A. R. Godinez-Cota, and G. Montemayor- 

 Lopez. 1997. Diagnosis de la pesqueria 

 de pelagicos menores del Golfo de Califor- 

 nia de 1991/92 a 1995/96. Informe Tecnico, 

 59 p. Centro Regional de Investigaciones 

 Pesqueras de Guaymas. INP. SEMARNAP. 

 Calle 20 No. 605 Sur Col. La Cantera. 

 Guavmas, Son. CP. 85400. 



